In order to shorten pilot overhead, an effective strategy is allowing orthogonal pilots to be reused among different users. Most of the existing works with pilot reuse (PR) mainly focus on multiple-cell scenarios, i.e., mobile users in the same cell use orthogonal pilots, and users in different cells reuse the same set of pilots [1]}, [2]}, [3]}, [4]}, [5]}. To the best of the authors' knowledge, only a few works have considered the strategy of PR within a cell [6]}, [7]}, [8]}, [9]}. In [6]}, the authors analyzed the feasibility of PR over spatially correlated massive MIMO channels with constrained channel angular spreads. Authors of [7]} and [8]} allowed D2D-Txs to reuse the pilots of CUs and proposed an interference-aided minimum-mean-square-error (MMSE) detector to suppress the D2D-to-cellular interference. [9]} also studied a D2D underlaid massive MIMO system with PR, but the performance of CUs was left out of consideration for simplicity. In contrast to these existing works, our work analyzes the achievable rate of both cellular and D2D links under PR, and proposes pilot scheduling as well as power control algorithms to optimize the system performance. The main contributions of this paper are summarized as follows:
